Neuroscience Letters 423 (2007) 68–72 Saccular stimulation of the human cortex: A functional magnetic resonance imaging study Tamaki Miyamoto a,b,∗ , Kikuro Fukushima a,b , Toshihisa Takada c , Catherine de Waele d , Pierre-Paul Vidal d a Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, Japan b Brain function research laboratory, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, Japan c Department of Oral Functional Science, Hokkaido University Graduate School of Dental Medicine, Sapporo, Hokkaido, Japan d Laboratoire de Neurobiologie des R´ eseaux Sensorimoteurs, UMR 7060, CNRS-Paris 5-Paris 7,Paris, France Received 11 October 2006; received in revised form 7 May 2007; accepted 1 June 2007 Abstract Recent imaging studies have reported the projection of semicircular canal signals onto wide regions of the cerebral cortex but little is known about otolith projections onto the cerebral cortex. We used functional magnetic resonance imaging (fMRI) to investigate the activation of the cortex by loud clicks that selectively stimulate the sacculus. Twelve normal volunteers were presented with auditory stimuli via an earphone containing a piezo electric element. High-intensity [maximum volume of 120 dB (SPL)] or low-intensity [maximum volume of 110 dB (SPL)] clicks were delivered at a frequency of 1Hz and lasted 1ms. We first checked that the high-intensity, but not low-intensity, clicks stimulated the sacculus by determining the vestibular evoked myogenic potentials. We then analyzed two task conditions (high- and low-intensity clicks) in a boxcar paradigm. We obtained gradient echo echo-planar images by using a 1.5 T MRI system. We analyzed the fMRI time series data with SPM2. High-intensity clicks activated wide areas of the cortex, namely, the frontal lobe (prefrontal cortex, premotor cortex, and frontal eye fields), parietal lobe (the region around the intraparietal sulcus, temporo-parietal junction, and paracentral lobule), and cingulate cortex. These areas are similar to those reported in previous imaging studies that analyzed the cortical responses to the activation of the semicircular canals. Thus, semicircular canal and otolith/saccular signals may be processed in similar regions of the human cortex. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Sacculus; Otolith; Vestibular; fMRI; Clicks; Human The maintenance of body equilibrium in a gravitational field (balance) and the capacity to orient oneself in the environment are essential for survival. Balance requires spatial control of the head and trunk position as well as control of the position of the head in relation to the trunk. At least, three modes of sensory signals – visual, proprioceptive and vestibular – are involved. Gaze and posture are thus stabilized by complex mul- tisensory integration. This process involves matching multiple internal representations of an external event (i.e. head and/or trunk rotation) based on inputs from the various sensory modes to intrinsic frames of reference in which appropriate motor com- ∗ Corresponding author at: Department of Physiology, Graduate School of Medicine, Hokkaido University, N15W7 Kita-Ku, Sapporo 060-8638, Japan. Tel.: +81 11 706 5040; fax: +81 11 706 5041. E-mail address: paf01635@nifty.com (T. Miyamoto). mands can be coded. Well-defined neuronal networks implement these complex sensorimotor transformations, which are known as the vestibular, cervical and optokinetic reflexes. These inter- nal representations are then passed onto various cortical areas via trisynaptic pathways [6]. The six semicircular ampullae and four otolithic maculae of the two labyrinths are vestibular sensory organs. The otolith organs detect gravity and linear acceleration of the head while the ampullae of the semicircular canals transduce angular accelera- tions of the head. Signals from second-order vestibular nuclear neurons are projected onto the thalamus, which in turn projects onto various regions of the cerebral cortex. Electrophysiological recordings in animals have shown that vestibular stimulation activates cortical neurons in area 2v [4], area 3a [24], the parieto-insular-vestibular cortex (PIVC) [16], the ventral intraparietal area (VIP) [3], the medial superior tem- poral area (MST) [29], the frontal eye fields (FEFs) [15], and the 0304-3940/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2007.06.036